1. Field of the Invention
This invention relates to solid electrochemical (electrolytic) cells and, more particularly, to nickel-coated aluminum current collectors for solid electrochemical cells in which the electrolyte is a polymeric network interpenetrated by an ionically conducting liquid.
2. State of the Art
Electrochemical cells containing an anode, a cathode and a solid, solvent-containing electrolyte are known in the art and are usually referred to as "solid batteries." See, for instance, U.S. Pat. Nos. 5,229,225, 5,238,758, 5,358,801, and 5,366,829. These cells offer a number of advantages over electrochemical cells containing a liquid electrolyte (i.e., "liquid batteries") including improved safety features.
In a typical solid electrochemical cell, a current collector is provided as a support for the cathode. For example, the cathode, which is often prepared in the form of a paste, may be spread onto the current collector and then cured by conventional methods to provide for a solid positive cathodic plate. The cathode (excluding the support) generally has a thickness of between about 20 and 150 .mu.m. Current collectors themselves are well known in the art and are commercially available. Generally, the art to date has employed current collectors for cathodes which are made of roughened nickel (electrolytically deposited nickel) on a nickel current collector. The current collectors are preferably attached to the surface of the cathode not facing the electrolyte but can also be attached to the anode. When the current collector is attached to the cathode, the cathode is interposed between the electrolyte and the current collector.
Current collectors such as nickel have been found to be highly effective in minimizing corrosion in the battery environment. However, while effective in function, nickel current collectors give rise to at least two significant drawbacks. First, nickel is a relatively expensive metal and thus, its use as a current collector appreciably adds to the cost of a solid electrochemical cell. Second, nickel is a relatively heavy metal. Indeed, nickel current collectors employed at the present time in solid electrochemical cells can take up half the weight of the ultimate laminate. This, of course, significantly reduces the energy density available per weight of the cell.
In an attempt to overcome the significant drawbacks associated with nickel current collectors, aluminum has been used to fabricate current collectors. Aluminum is attractive in view of its low cost and low density, which are the problems which have been encountered with nickel. Nonetheless, aluminum has not proven itself to be a completely suitable substitute because it has been found to corrode over time in the battery environment.